Power transmission apparatus, control method, and computer-readable storage medium

ABSTRACT

A power transmission apparatus configured to wirelessly transmit power to a power reception apparatus executes, when wirelessly transmitting power, detection processing for detecting an object different from the power reception apparatus, using a power loss, obtains, from the power reception apparatus, reference value information regarding a reference value of received power used to obtain the power loss, and performs a specific control after the power loss has been obtained and in a case where a predetermined time has elapsed since a predetermined timing associated with a timing at which information is obtained from the power reception apparatus, without obtaining the reference value information that is valid, the specific control being a control to prevent a power transmission output from being increased, regardless of received power in the power reception apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Patent ApplicationNo. PCT/JP2020/032926, filed Aug. 31, 2020, which claims the benefit ofJapanese Patent Application No. 2019-161463 filed Sep. 4, 2019, both ofwhich are hereby incorporated by reference herein in their entireties.

BACKGROUND Technical Field

The present disclosure relates to a technique for controllingtransmission power and received power in wireless power transfer.

Background Art

Techniques for wireless power transfer systems have been widelydeveloped. Japanese Patent Laid-Open No. 2015-165761 describes a methodby which a foreign object, which is an object different from a powerreception apparatus, is detected during power transmission and receptioncompliant with a standard (WPC standard) stipulated by the WirelessPower Consortium (WPC), which is a standardization organization ofwireless charging standards. In this method, received power at a timepoint in the past and received power at the present time point arecompared, and it is determined that a foreign object is present if thereis no increase in the received power despite the fact that control toincrease the transmission power has been performed, or if there is nodecrease in the received power despite the fact that control to reducethe transmission power has been performed.

It can be envisaged that, due to a change in the power transmission andreception environment, for example, the received power gradually changeseven if the same power is transmitted. At this time, if, despite thefact that there is a significant time difference between a time point inthe past and the present time point, foreign object detection isperformed using information at the time point in the past, the accuracyof the foreign object detection may be reduced. This may result invarious problems that can reduce convenience, including, for example,stopping of charging due to erroneous detection, and a temperatureincrease caused by failing to detect a foreign object that is present.

SUMMARY

The present disclosure provides a technique for improving convenience ofwireless power transfer.

A power transmission apparatus according to an aspect of the presentdisclosure includes: a power transmission unit configured to wirelesslytransmit power to a power reception apparatus; a communication unitconfigured to communicate with the power reception apparatus; aprocessing unit configured to execute, when wirelessly transmittingpower using the power transmission unit, detection processing fordetecting an object different from the power reception apparatus, usinga power loss; an obtaining unit configured to obtain, using thecommunication unit, from the power reception apparatus, reference valueinformation regarding a reference value of received power that is usedto obtain the power loss; and a control unit configured to perform aspecific control after the power loss has been obtained and in a casewhere a predetermined time has elapsed since a predetermined timingassociated with a timing at which information is obtained from the powerreception apparatus, without obtaining the reference value informationthat is valid, the specific control being a control to prevent an outputpower using the power transmission unit from being increased, regardlessof received power of the power reception apparatus.

Further features of the present disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure and, together with the description, serve to explainprinciples of the present disclosure.

FIG. 1 is a diagram showing a configuration of a wireless chargingsystem.

FIG. 2 is a diagram showing a configuration example of a power receptionapparatus.

FIG. 3 is a diagram showing a configuration example of a powertransmission apparatus.

FIG. 4 is a flowchart illustrating an example of a flow of processingexecuted by the power transmission apparatus.

FIG. 5 is a flowchart illustrating an example of a flow of powertransmission control processing executed by the power transmissionapparatus.

FIG. 6A is a flowchart illustrating an example of a flow of timeoutprocessing executed by the power transmission apparatus.

FIG. 6B is a flowchart illustrating the example of a flow of timeoutprocessing executed by the power transmission apparatus.

FIG. 7 is a flowchart illustrating an example of a flow of processingexecuted by the power reception apparatus.

FIG. 8 is a flowchart illustrating an example of a flow of powerreception control processing executed by the power reception apparatus.

FIG. 9A is a diagram showing a communication sequence in a Calibrationphase.

FIG. 9B is a diagram showing a communication sequence for deviceauthentication.

FIG. 10A is a diagram showing a first example of a flow of processingexecuted in the system.

FIG. 10B is a diagram illustrating the first example of a flow ofprocessing executed in the system.

FIG. 11A is a diagram showing a second example of a flow of processingexecuted in the system.

FIG. 11B is a diagram showing the second example of a flow of processingexecuted in the system.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe attached drawings. Note, the following embodiments are not intendedto limit the scope of the present disclosure. Multiple features aredescribed in the embodiments, but limitation is not made to the presentdisclosure that requires all such features, and multiple such featuresmay be combined as appropriate. Furthermore, in the attached drawings,the same reference numerals are given to the same or similarconfigurations, and redundant description thereof is omitted.

(Configuration of System)

FIG. 1 shows a configuration example of a wireless charging system(wireless power transfer system) according to the present embodiment. Inan example, the present system includes a power reception apparatus 101and a power transmission apparatus 102. In the following, the powerreception apparatus 101 may be referred to as the “RX”, and the powertransmission apparatus 102 may be referred to as the “TX”. The RX is anelectronic apparatus that receives power from the power transmissionapparatus 102, and charges an internal battery. The TX is an electronicapparatus that wirelessly transmits power to the RX placed on a chargingstand 103. A range 104 indicates a range in which the RX can receivepower transmitted from the TX. The RX and the TX may have the functionfor executing an application other than wireless charging. One exampleof the RX is a smartphone, and one example of the TX is an accessoryapparatus for charging the smartphone. The RX and the TX may each be astorage apparatus such as a hard disk apparatus and a memory apparatus,or may be an information processing apparatus such as a personalcomputer (PC). Alternatively, the RX and the TX each may be an imageinput apparatus such as an image capturing apparatus (a camera, a videocamera, etc.) and a scanner, or may be an image output apparatus such asa printer, a copier, and a projector. Alternatively, the TX may be asmartphone. In this case, the RX may be another smartphone, or may be aperipheral apparatus such as a wireless earphone. Alternatively, the RXmay be an automobile. Alternatively, the TX may be a charger installedin a console or the like in the automobile.

The present system performs wireless power transfer using anelectromagnetic induction method for wireless charging in accordancewith a WPC standard prescribed by the WPC (Wireless Power Consortium).That is, the RX and the TX perform wireless power transfer for wirelesscharging in accordance with the WPC standard between a power receptioncoil of the RX and a power transmission coil of the TX. The method forthe wireless power transfer is not limited to the method defined in theWPC standard, and may be another electromagnetic induction method, amagnetic resonance method, an electric field resonance method, amicrowave method, or a method using laser or the like. Although wirelesspower transfer is used for wireless charging in the present embodiment,wireless power transfer may be performed for a usage other than wirelesscharging.

In the WPC standard, power that is guaranteed when the RX receives powerfrom the TX is defined by a value called “Guaranteed Power” (hereinafterreferred to as a “GP”). The GP represents a value of power guaranteed tobe output to a load, such as a charging circuit, of the RX even if thepower transmission efficiency between the power reception coil and thepower transmission coil is reduced, for example, owing to variation inthe positional relationship between the RX and the TX. For example, whenthe GP is 5 W, the TX performs power transmission while performingcontrol such that 5 W can be output to the load in the RX, even if thepower transmission efficiency is reduced owing to variation in thepositional relationship between the power reception coil and the powertransmission coil.

The RX and the TX according to the present embodiment performcommunication for power transmission/reception control in accordancewith the WPC standard, and communication for device authentication.Here, the communication for power transmission/reception control inaccordance with the WPC standard will be described.

The WPC standard defines a plurality of phases, including a PowerTransfer phase in which power transfer is performed, and phases beforethe actual power transfer is performed, and communication for powertransmission/reception control necessary for each phase is performed.The phases before power transfer includes a Selection phase, a Pingphase, a Configuration phase, a Negotiation phase, and a Calibrationphase. In the Selection phase, the TX intermittently transmits an AnalogPing, and detects that an object is present in a power transmittablerange (e.g., that the power reception apparatus 101, a conductor strip,or the like is placed on the charging stand 103). In the Ping phase, theTX transmits a Digital Ping, and recognizes that the detected object isthe RX by receiving a response from an RX that has received the DigitalPing. In the Configuration phase, the RX notifies the TX ofidentification information and capability information. In theNegotiation phase, a negotiation for determining a value of the GP basedon a value of GP that is requested from the RX, the power transmissioncapability of the TX, or the like is performed. In the Calibrationphase, the RX notifies the TX of a received power value in accordancewith the WPC standard, and the TX performs adjustment for performingforeign object detection during power transmission. In the PowerTransfer phase, control for, for example, continuing power transmission,and stopping power transmission due to an error or full charge isperformed. The TX and the RX perform communication for these powertransmission and reception controls, using In-band communication inwhich signals are superposed using the same antennas (coils) used forwireless power transfer in accordance with the WPC standard. The rangein which the In-band communication in accordance with the WPC standardcan be performed between the TX and the RX is substantially the same asthe power transmittable range. That is, in FIG. 1, the range 104indicates a range in which wireless power transfer and In-bandcommunication can be performed using the power transmission andreception coils of the TX and the RX. In the following description, theRX being “placed” means the RX having entered inside the range 104, andincludes the RX in the state of not being actually placed on thecharging stand 103.

The TX and the RX may perform communication (Out-of-band communication)for power transmission/reception control, using antennas (coils) thatare different from those used for wireless power transfer. Examples ofthe communication using antennas (coils) that are different from thoseused for wireless power transfer include a communication methodcompliant with the Bluetooth (registered trademark) Low Energy standard.Alternatively, another communication method such as the IEEE 802.11standard wireless LAN (e.g., Wi-Fi (registered trademark), ZigBee, andNFC (Near Field Communication) may be used. The communication usingantennas (coils) that are different from those used for wireless powertransfer may be performed with a frequency that is different from thatfrequency used for wireless power transfer.

In the present embodiment, prior to determining a GP, the RX performschallenge-response communication using an electronic certificate withthe TX, and performs device authentication on the TX. That is, the RXperforms communication for device authentication for the TX. Then, basedon a result of the device authentication, the RX determines a GP that isto be requested from the TX in the Negotiation phase described above.For example, the RX determines a GP that is to be requested from the TXfor which the device authentication has succeeded, as 15 W, anddetermines the GP that is to be requested from the TX for which thedevice authentication has not succeeded, as 5 W. The GP that is to berequested from the TX is not limited to a combination of 15 W and 5 W.For example, it is possible to use a combination of any values in whicha GP that is to be requested from a TX for which the deviceauthentication has succeeded is larger than a GP that is to be requestedfrom a TX for which the device authentication has not succeeded. Thus,the RX may perform power transmission/reception with a large GP onlywith a TX for which device authentication has succeeded. By determiningthe GP based on a result of the device authentication in this manner,the RX is allowed to receive power with a large GP only from a TX thathas passed a predetermined test defined in the WPC standard or the like,and that is acknowledged as being capable of transmitting power with alarge GP.

(Apparatus Configuration)

Next, a configuration of the power reception apparatus 101(RX) and thepower transmission apparatus 102 (TX) according to the presentembodiment will be described. The components described below are merelyexamples. Some (possibly all) of the described components may bereplaced by another configuration serving the same function, or may beomitted, and a further component may be added to the describedcomponents. Furthermore, one block described in the followingdescription may be divided into a plurality of blocks, and a pluralityof blocks may be integrated into one block.

FIG. 2 is a diagram showing a configuration example of the RX accordingto the present embodiment. In an example, the RX includes a control unit201, a battery 202, a power reception unit 203, a detection unit 204, apower reception coil 205, a communication unit 206, a display unit 207,an operation unit 208, a memory 209, a timer 210, and a charging unit211.

The control unit 201 performs overall control of the RX by executing acontrol program stored in the memory 209, for example. In an example,the control unit 201 performs control necessary for the deviceauthentication and the power reception in the RX. The control unit 201may perform control for executing an application other than wirelesspower transfer. The control unit 201 includes, for example, one or moreprocessors such as a central processing unit (CPU) and a microprocessing unit (MPU). The control unit 201 may include hardwarededicated to specific processing such as an application specificintegrated circuit (ASIC), and an array circuit compiled to executepredetermined processing, such as a field-programmable gate array(FPGA). The control unit 201 causes the memory 209 to store informationthat is to be stored while various types of processing are beingexecuted. In addition, the control unit 201 may measure time using thetimer 210.

The battery 202 supplies, to the entire RX, power required to performcontrol, power reception, and communication. In addition, the battery202 stores the power received via the power reception coil 205. In thepower reception coil 205, induced electromotive force is generated byelectromagnetic waves that have been emitted from a power transmissioncoil 305 of the TX, and the power reception unit 203 obtains the powergenerated in the power reception coil 205. The power reception unit 203obtains alternating-current power that has been generated throughelectromagnetic induction in the power reception coil 205. Then, thepower reception unit 203 converts the alternating-current power intodirect-current power, or alternating-current power at a predeterminedfrequency, and outputs the power to the charging unit 211 that executesprocessing for charging the battery 202. That is, the power receptionunit 203 supplies power to a load of the RX. The GP described above ispower that is guaranteed to be output from the power reception unit 203.

The detection unit 204 detects, in accordance with the WPC standard,whether or not the RX is placed in the range 104 in which power can bereceived from the TX. For example, the detection unit 204 detects avoltage value or a current value of the power reception coil 205 whenthe power reception unit 203 has received a Digital Ping of the WPCstandard via the power reception coil 205. For example, the detectionunit 204 may determine that the RX is placed in the range 104 if thevoltage falls below a predetermined voltage threshold, or the currentvalue exceeds a predetermined current threshold.

The communication unit 206 performs control communication in accordancewith the WPC standard as described above with the TX, using In-bandcommunication. The communication unit 206 demodulates electromagneticwaves that have been input from the power reception coil 205, to obtainthe information transmitted from the TX, and superposes, on theelectromagnetic waves, the information to be transmitted to the TX byperforming load modulation on the electromagnetic waves, therebycommunicating with the TX. That is, the communication performed by thecommunication unit 206 is performed by superposing the information onthe power transmitted from the power transmission coil 305 of the TX.The communication unit 206 may perform Out-of-band communication withthe TX.

The display unit 207 presents the information to the user by any methodsuch as a visual, audio, or tactile method. For example, the displayunit 207 notifies the user of the state of the RX, or the state of thewireless power transfer system including the TX and the RX as shown inFIG. 1. The display unit 207 includes, for example, a liquid crystaldisplay, an LED, a speaker, a vibration generation circuit, or anothernotification device. The operation unit 208 has accepting functionalityof accepting an operation to the RX from the user. The operation unit208 includes, for example, an audio input device such as a button, akeyboard, and a microphone, a motion detection device such as anacceleration sensor and a gyrosensor, or another input device. A devicein which the display unit 207 and the operation unit 208 are integratedinto one piece, such as a touch panel, may be used. As described above,the memory 209 stores various types of information. The memory 209 maystore information obtained by a functional unit that is different fromthe control unit 201. The timer 210 measures time using, for example, acount up timer that measures the time elapsed from a time at which thetimer was started, a countdown timer that counts down from a set time,or the like.

FIG. 3 is a diagram showing a configuration example of the TX accordingto the present embodiment. In an example, the TX includes a control unit301, a power unit 302, a power transmission unit 303, a detection unit304, a power transmission coil 305, a communication unit 306, a displayunit 307, an operation unit 308, a memory 309, and a timer 310.

The control unit 301 performs overall control of the TX by executing acontrol program stored in the memory 309, for example. In an example,the control unit 301 performs control necessary for the deviceauthentication and the power transmission in the TX. The control unit301 may perform control for executing an application other than wirelesspower transfer. The control unit 301 includes, for example, one or moreprocessors such as a central processing unit (CPU) and a microprocessing unit (MPU). The control unit 301 may include hardwarededicated to specific processing such as an application specificintegrated circuit (ASIC), and an array circuit compiled to executepredetermined processing, such as a field-programmable gate array(FPGA). The control unit 301 causes the memory 309 to store informationthat is to be stored while various types of processing are beingexecuted. In addition, the control unit 301 may measure time using thetimer 310.

The power unit 302 supplies, to the entire TX, power required to performcontrol, power transmission, and communication. The power unit 302 is acommercial power supply or a battery, for example.

The power transmission unit 303 converts direct current oralternating-current power that is input from the power unit 302, intoalternating-current frequency power with a frequency band used forwireless power transfer, and inputs the alternating-current frequencypower to the power transmission coil 305, thereby generatingelectromagnetic waves that are to be received by the RX. The frequencyof the alternating-current power generated by the power transmissionunit 303 is several hundred kHz (e.g., 110 kHz to 205 kHz). Inaccordance with an instruction from the control unit 301, the powertransmission unit 303 inputs the alternating-current frequency power tothe power transmission coil 305 such that electromagnetic waves fortransmitting power to the RX are output from the power transmission coil305. The power transmission unit 303 regulates the voltage (transmissionvoltage) or the current (transmission current) that is input to thepower transmission coil 305, thereby controlling the intensity of theelectromagnetic waves to be output. When the transmission voltage or thetransmission current is increased, the intensity of the electromagneticwaves is increased. When the transmission voltage or the transmissioncurrent is reduced, the intensity of the electromagnetic waves isreduced. In accordance with an instruction from the control unit 301,the power transmission unit 303 controls the output of thealternating-current frequency power such that the power transmissionfrom the power transmission coil 305 is started or stopped.

The detection unit 304 detects, in accordance with the WPC standard,whether or not an object is present in the range 104. For example, thedetection unit 304 detects a voltage value or a current value of thepower transmission coil 305 when the power transmission unit 303 hastransmitted an Analog Ping of the WPC standard via the powertransmission coil 305. Then, the detection unit 304 may determine thatan object is present in the range 104 if the voltage falls below apredetermined voltage value, or the current value exceeds apredetermined current value. As for determination as to whether theobject is the RX or any other foreign object, the object is determinedto be the RX if a predetermined response has been received to a DigitalPing subsequently transmitted by the communication unit 306 usingIn-band communication.

The communication unit 306 performs control communication in accordancewith the WPC standard as described above with the RX, using In-bandcommunication. The communication unit 306 modulates electromagneticwaves that are output from the power transmission coil 305, andtransmits the information to the RX. The communication unit 306demodulates the electromagnetic waves that have been output from thepower transmission coil 305 and modulated in the RX, to obtain theinformation transmitted by the RX. That is, in the communicationperformed by the communication unit 306, the information is superposedon the power transmitted from the power transmission coil 305. Thecommunication unit 306 may perform Out-of-band communication with theRX.

The display unit 307 presents the information to the user by any methodsuch as a visual, audio, or tactile method. For example, the displayunit 307 notifies the user of information indicating the state of theTX, or the state of the wireless power transfer system including the TXand the RX as shown in FIG. 1. The display unit 307 includes, forexample, a liquid crystal display, an LED, a speaker, a vibrationgeneration circuit, or another notification device. The operation unit308 has accepting functionality of accepting an operation to the TX fromthe user. The operation unit 308 includes, for example, an audio inputdevice such as a button, a keyboard, and a microphone, a motiondetection device such as an acceleration sensor and a gyrosensor, oranother input device. A device in which the display unit 307 and theoperation unit 308 are integrated into one piece, such as a touch panel,may be used. As described above, the memory 309 stores various types ofinformation. The memory 309 may store information obtained by afunctional unit that is different from the control unit 301. The timer310 measures time using, for example, a count up timer that measures thetime elapsed from a time at which the timer was started, a count downtimer that counts down from a set time, or the like.

(Flow of Processing Executed by Power Transmission Apparatus)

Next, an example of a flow of processing executed by the TX will bedescribed. FIG. 4 shows an example of a flow of processing executed bythe TX. The present processing may be implemented, for example, by thecontrol unit 301 of the TX executing a program read from the memory 309.At least part of the following processing may be implemented withhardware. The hardware in this case may be implemented, for example, byusing a predetermined compiler to automatically generate, from a programfor implementing processing steps, a dedicated circuit including a gatearray circuit such as an FPGA. The present processing may be executed inresponse to the TX being turned on, in response to the user of the TXinputting an instruction to start a wireless charging application, or inresponse to the TX being connected to the commercial power supply andreceiving the power therefrom. Alternatively, the present processing maybe started using another trigger.

In the present processing, the TX first executes processing defined as aSelection phase and a Ping phase in the WPC standard, and waits for theRX to be placed (S401). In these phases, the TX intermittently transmitan Analog Ping of the WPC standard in a repeated manner, and detects anobject that is present in the power transmittable range. Then, if it isdetected that an object is present in the power transmittable range, theTX transmits a Digital Ping of the WPC standard. If a predeterminedresponse has been received to the Digital Ping, the TX determines thatthe detected object is the RX, and that the RX is placed on the chargingstand 103.

If it is detected in S401 that the RX is placed, the TX obtainsidentification information and capability information from the RX, usingcommunication in the Configuration phase defined in the WPC standard(S402). Here, the identification information of the RX includes aManufacturer Code and a Basic Device ID. The capability information ofthe RX includes an information element capable of specifying the versionof the corresponding WPC standard, a Maximum Power Value, which is avalue specifying a maximum power that the RX can supply to a load, andinformation indicating whether or not the RX has the Negotiationfunction of the WPC standard. These are merely examples, and theidentification information and the capability information of the RX maybe replaced by other information, or may include other information inaddition to the above-described information. For example, theidentification information may be any other identification informationcapable of identifying an individual RX, such as a Wireless Power ID.The TX may obtain the identification information and the capabilityinformation of the RX by a method other than the communication in theConfiguration phase of the WPC standard.

Subsequently, the TX performs a Negotiation with the RX, usingcommunication in the Negotiation phase defined in the WPC standard, todetermine a value of the GP (S403). The procedure performed in S403 isnot limited to communication in the Negotiation phase of the WPCstandard, and another procedure for determining the GP may be performed.If the TX obtains (e.g., in S402) information indicating that the RXdoes not correspond to the Negotiation phase, the TX may determine avalue of the GP to be a small value (e.g., a value that is predefined inthe WPC standard), without performing communication in the Negotiationphase.

After determining the GP, the TX performs calibration based on thedetermined GP (S404). Calibration is processing for calibrating, forpower that has been transmitted by the TX to the RX, the correlationbetween a value of power transmission output, which is a value measuredby the TX in self apparatus, and a value of received power, which is avalue measured by the RX in self apparatus. For example, the TXestimates a power loss that can be determined as a difference betweenthe value of power transmission output and the value of received power,based on the value of received power serving as a reference value forcalibration, received from the RX, and the value of power transmissionoutput that is set when the received power serving as the referencevalue is obtained. In the calibration processing, the transmission powerof the TX and the received power of the RX may be obtained when thestates of the RX are two states that are different from each other.Then, using the two sets of transmission power and received power,parameters for performing calibration for the received power or thetransmission power during the actual wireless power transmission may becalculated. The parameters refer to a value of slope and a value ofintercept when the correlation between the transmission power and thereceived power is graphically represented by a linear function. Thecombination used for calculating such parameters is not limited to setsof transmission power and received power, and may be sets oftransmission power and a power loss, or may be sets of received powerand a power loss.

As shown in FIG. 9A, communication in the Calibration phase of the WPCstandard is performed in the calibration. In this processing, as shownin FIG. 9A, first, the RX transmits, to the TX, information (hereinafterreferred to as “first calibration reference value information”)including received power in a light-load state that serves as a firstcalibration reference value (F901). Here, the first calibrationreference value information is transmitted and received using, forexample, Received Power (mode 1), which is a message defined in the WPCstandard. However, another message may be used. The TX determines, basedon its own power transmission state, whether or not to accept the firstcalibration reference value information. The TX transmits, to the RX, apositive acknowledgement (ACK) if the TX accepts the first calibrationreference value information, and a negative acknowledgement (NAK) if theTX does not accept the first calibration reference value information(F902). Here, for example, the TX accepts the notification if the TXdetermines that its own power transmission state is stable, and does notaccept the notification if the TX determines that its own powertransmission state is unstable. The calibration reference valueinformation accepted by the TX may be referred to as valid calibrationreference value information. If the RX receives a NAK from the TX, theRX transmits the first calibration reference value information again. Onthe other hand, if the RX receives an ACK from the TX, the RX transmits,to the TX, information (hereinafter may be referred to as “secondcalibration reference value information”) including received power in aload connection state that serves as a second calibration referencevalue (F903). Here, the second calibration reference value informationis transmitted and received using, for example, Received Power (mode 2),which is a message defined in the WPC standard. However, another messagemay be used. The TX determines, based on its own power transmissionstate, whether or not to accept the second calibration reference valueinformation. As in F902, the TX transmits. to the RX, an ACK if the TXaccepts the second calibration reference value information, and a NAK ifthe TX does not accept the second calibration reference valueinformation (F904). If the RX receives a NAK from the TX, the RXtransmits the second calibration reference value information again. Upontransmitting the ACK to the RX, the TX specifies, based on the receivedpowers included in the first calibration reference value information andthe second calibration reference value information, the respective powerlosses when the two reference values are used. Then, the TX estimates apower loss when received power of a value that is different from the tworeference values is received, using a linear interpolation based on thetwo specified power loss values, for example. The TX may determine thatthe calibration has failed if the TX is unable to transmit an ACK as aresponse to the second calibration reference value information within apredetermined time after the completion of the Negotiation phase (S403),and may stop the power transmission. The calibration may be performed bya method other than that of the WPC standard.

After the completion of the calibration, the TX starts the powertransmission (S405). The power transmission is performed throughprocessing in the Power Transfer phase of the WPC standard. However, thepower transmission is not limited thereto, and may be performed by amethod other than that of the WPC standard.

Subsequently, the TX performs communication for device authenticationwith the RX (S406). Here, the communication for device authenticationperformed between the RX and the TX will be described with reference toFIG. 9B. It is assumed that the device authentication in the presentembodiment is challenge-response device authentication using anelectronic certificate, and that the RX authenticates the TX. The TX mayauthenticate the RX, or both the TX and the RX may authenticate thecounterpart apparatus. The RX operates as an initiator that transmits achallenge text to the TX, and the TX operates as a responder thatencrypts the challenge text received from the RX, and transmits theencrypted challenge text to the RX. First, the RX transmits aGET_DIGESTS message to the TX (F911). GET_DIGESTS is a messagerequesting information regarding the electronic certificate owned by thereceiver (TX) of the message. In response to GET_DIGESTS, the TXtransmits DIGESTS to the RX (F912). DIGESTS is a message includinginformation regarding the electronic certificate owned by thetransmitter (TX) of the message. Subsequently, the RX transmits, to theTX, a GET_CERTIFICATE message requesting detailed information regardingthe electronic certificate (F913). In response to GET_CERTIFICATE fromthe RX, the TX transmits CERTIFICATE to the RX (F914). Then, the RXtransmits, to the TX, a CHALLENGE message including the challenge text(F915), and the TX transmits, to the RX, CHALLENGE_AUTH resulting fromencrypting the challenge text received from the RX (F916). The RXdetermines that the device authentication has succeeded if thecorrectness of CHALLENGE_AUTH received from the TX is verified, anddetermines that the device authentication has failed if the correctnesscannot be verified. Upon completion of this determination, the deviceauthentication processing ends.

If the initiator (RX) has received a message indicating that thecounterpart apparatus (TX) does not support communication for deviceauthentication, the initiator (RX) determines that the counterpartapparatus does not support device authentication. If the initiator (RX)has not received a response during the communication, the initiator (RX)may perform a retry, for example, by resending a message for obtainingthe response, or may determine that the counterpart apparatus (TX) doesnot support device authentication. The RX may be configured to not toperform communication for device authentication with a TX that does notsupport device authentication, and not to determine a result of deviceauthentication as successful. Here, it is assumed that deviceauthentication has succeeded in S406.

Referring back to FIG. 4, the TX redetermines, together with the RX, avalue of the GP through communication in the Negotiation phase definedin the WPC standard (S407). Here, because the device authentication inS406 has succeeded, the value of the GP is determined to be a value(e.g., 15 W) greater than 5 W. After redetermining the GP, the TXrepeatedly executes power transmission control processing (S408). If EndPower Transfer of the WPC standard has been received from the RX, the TXends processing executed in whatever processing phase, in accordancewith the WPC standard, and stops the power transmission before returningto the Selection phase in S401. End Power Transfer is also transmittedfrom the RX if a fully charged state has been reached. Accordingly, theTX returns to the Selection phase in S401.

An example of a flow of the power transmission control processingexecuted by the TX in S408 will be described with reference to FIG. 5.The present processing may be implemented, for example, by the controlunit 301 of the TX executing a program read from the memory 309. Atleast part of the following processing may be implemented with hardware.The hardware in this case may be implemented, for example, by using apredetermined compiler to automatically generate, from a program forimplementing processing steps, a dedicated circuit including a gatearray circuit such as an FPGA.

Using the start of the processing as a trigger, the TX starts a timer tothe completion of calculation of an estimated value of power loss(S501). The timer may be started, using the start of the presentprocessing as a trigger, or in other words, using, as a trigger, thetransmission of an ACK to Specific Request (hereinafter referred to as“SRQ/en”) defined in the WPC standard and indicating the completion ofcommunication in the Negotiation phase. However, the present disclosureis not limited thereto, and the timer may be started, for example,using, as a trigger, the completion of calculation of the estimatedvalue of power loss, or the transmission of an ACK to the receivedcalibration reference value information. Alternatively, the timer may bestarted at a timing at which SRQ/en is received. After starting thetimer, the TX determines whether or not a power transmission outputchange instruction has been received from the RX (S502). Here, the powertransmission output change instruction is performed by including ControlError Value, which is a value indicating a change amount of the voltage,in the Control Error message of the WPC standard. In Control ErrorValue, a positive value is stored if the power transmission output is tobe increased, a negative value is stored if the power transmissionoutput is to be reduced, and 0 is stored if the power transmissionoutput is not changed. If the power transmission output changeinstruction has been received (YES in S502), the TX changes the powertransmission output based on the instructed change amount (S503), andadvances the processing to S504. On the other hand, if the powertransmission output change instruction has not been received (NO inS502), the TX advances the processing to S504, without doing anything.

In S504, the TX determines whether or not received power information hasbeen received from the RX. Here, the received power information isinformation including received power that has been actually received inthe RX at that point of time. The received power information istransmitted and received using a Received Power (mode 0) message definedin the WPC standard. However, the present disclosure is not limitedthereto. If the received power information has been received (YES inS504), the TX transmits an ACK (S505), and advances the processing toS506. On the other hand, if the received power information has not beenreceived (NO in S504), the TX advances the processing to S506, withoutdoing anything.

In S506, the TX determines whether or not enhanced calibration referencevalue information has been received from the RX. Here, the enhancedcalibration reference value information is information includingreceived power in a load connection state that serves a reference valuefor additional calibration for calculating an estimated value of powerloss. If the enhanced calibration reference value information has beenreceived (YES in S506), the TX advances the processing to S507, and ifthe enhanced calibration reference value information has not beenreceived (NO in S506), the TX advances the processing to S511. In S507,the TX determines whether or not to accept the enhanced calibrationreference value information received in S506. Here, the TX may determinewhether or not to accept the enhanced calibration reference valueinformation according to whether or not its own power transmission stateis stable. However, the present disclosure is not limited thereto. Forexample, the TX may determine not to accept the enhanced calibrationreference value information if the power loss in the received powerindicated by the enhanced calibration reference value informationdeviates from a calculated estimated value of power loss by apredetermined value or more.

If the TX accepts the enhanced calibration reference value information(YES in S507), the TX calculates an estimated value of power loss basedon the received power indicated by the enhanced calibration referencevalue information (S508), and transmits an ACK to the RX (S509). Thecalculation of an estimated value of power loss and the transmission ofan ACK may be performed in the reversed order, or may be performedsimultaneously (their processing periods may at least partiallyoverlap). Then, the TX resets the timer (S513), and ends the processing.The estimated value of power loss is estimated based on, for example, afirst power loss at first received power indicated by the enhancedcalibration reference value information received in S506, and a secondpower loss estimated based on second received power indicated by theprevious calibration reference value information. For example, from avalue L1 of the first power loss corresponding to first received powerP1, and a value L2 of the second power loss corresponding to secondreceived power P2, the value of a power loss corresponding to receivedpower P between P1 and P2 is calculated as (L2−L1)/(P2−P1)×(P−P1)+L1.However, the method for estimating a power loss is not limited to linearinterpolation. For example, based on at least one calibration referencevalue information received in an after the Calibration phase, theestimated value of power loss may be calculated using statisticalanalysis such as linear approximation and polynomial approximation. Theestimation method may be selected from these estimation methodsaccording to the number of pieces of available calibration referencevalue information, and the computational resources of the TX.Accordingly, in the case where there are sufficient computationalresources, a highly accurate estimated value can be calculated byperforming statistical analysis using a larger number of pieces ofcalibration reference value information. In the case where computationalresources are scarce, the computation time required for the calculationcan be reduced by performing simple estimation such as linearinterpolation.

On the other hand, if the TX does not accept the enhanced calibrationreference value information (NO in S507), the TX transmits a NAK to theRX (S510), and determines whether or not a timeout has occurred (S511).The TX may determine whether or not a timeout has occurred, based onwhether or not the calculation of the estimated value of power loss hasbeen completed within a predetermined time after the timer has startedin S501. That is, the TX may determine that a timeout has occurred, if apredetermined time has elapsed without receiving the enhancedcalibration reference value information from the RX, or if apredetermined time has elapsed without transmitting an ACK to theenhanced calibration reference value information. Instead of or inaddition to measuring time with the timer, the TX may determine whetheror not the number of times of reception of the power transmission outputchange instruction received from the RX, or the number of times ofreception of predetermined information that is different from thecalibration reference value information, such as the received powerinformation received from the RX, has become greater than or equal to apredetermined number of times. For example, in S501, when starting thetimer, or instead of starting the timer, the TX may reset the number oftimes of reception of instructions or information to 0, count up thenumber of times of reception each time the TX receives an instruction orinformation, and determine, in S511, whether or not the number of timeshas reached a predetermined number of times. Instead of or in additionto measuring time with the timer, the TX may determine whether or notthe number of times of transmission of NAK to the received enhancedcalibration reference value information has become greater than or equalto a predetermined number of times. In this case as well, the TX mayreset the number of times of transmission of NAK to 0 in S501, count upthe number of times of transmission each time the TX transmits an NAK,and determine, in S511, whether or not the number of times has reached apredetermined number of times. If it is determined that a timeout hasoccurred (YES in S511), the TX executes timeout processing (S512). Uponcompletion of the timeout processing, the TX resets the timer (S513),and ends the present processing. The timeout processing in S512 will bedescribed later. On the other hand, if it is determined that a timeouthas not occurred (NO in S511), the TX returns the processing to S502.

As described above, the TX repeatedly executes the processing shown inFIG. 5. By repeatedly executing this processing, and sequentiallyupdating the estimated value of power loss using the enhancedcalibration reference value information, it is possible to prevent areduction in the accuracy of foreign object detection by performing theforeign object detection based on the most recent estimated value ofpower loss. As a result, it is possible prevent suspension of chargingdue to erroneous detection of a foreign object, and a temperatureincrease caused by failing to detect a foreign object that is present,thus improving convenience. If the timer is reset in S513, the startingof the timer in S501 may be performed at that point in time. That is,the resetting and the restarting of the timer may be performed at thesame timing. If valid calibration reference value information has beenobtained, the timer may be reset, for example, at a predetermined timingassociated with the timing of obtaining calibration reference valueinformation, such as a timing at which the calibration reference valueinformation is obtained, a timing at which an estimated value of powerloss is calculated, and a timing at which an ACK is transmitted. Duringthe timeout processing, the timer may be reset at a predetermined timingsuch as a reception timing of received power information indicatingreceived power that has been reduced to a target value, a receptiontiming of valid enhanced calibration reference value information, and atransmission timing of an ACK to these pieces of information.

Next, a flow of the timeout processing executed in S512 of FIG. 5 willbe described with reference to FIGS. 6A and 6B. The present processingmay be implemented, for example, by the control unit 301 of the TXexecuting a program read from the memory 309. At least part of thefollowing processing may be implemented with hardware. The hardware inthis case may be implemented, for example, by using a predeterminedcompiler to automatically generate, from a program for implementingprocessing steps, a dedicated circuit including a gate array circuitsuch as an FPGA.

After starting the processing, the TX determines whether or not a powertransmission output change instruction has been received from the RX(S601). If the power transmission output change instruction has beenreceived (YES in S601), the TX advances the processing to S602, and ifthe power transmission output change instruction has not been received(NO in S601), the TX advances the processing to S605. In S602, the TXdetermines whether the power transmission output change instruction isan instruction to increase the power transmission output, or in otherwords, whether a positive value is included in Control Error Value inthe Control Error message, for example. If it is determined that thepower transmission output change instruction indicates the increase ofthe power transmission output (YES in S602), the TX does not change thepower transmission output (S603), and advances the processing to S605.That is, the TX is configured to not to follow the power transmissionoutput change instruction to increase the power transmission output, ina situation where it is determined that a timeout has occurred, forexample, based on that a certain time has elapsed without obtaining anynew calibration reference value after updating the calibration referencevalue. In a situation where the accuracy of foreign object detection hasbeen reduced as a result of the calibration reference value informationlacking accuracy after an elapse of a long time after updating thecalibration reference value, the TX may determine that no foreign objectis present despite that the foreign object is present. Accordingly, itis possible to prevent a temperature increase or the like by configuringthe TX to not to increase the power transmission output in anenvironment in which a foreign object is present, but there is apossibility that the presence thereof cannot be detected. On the otherhand, if it is determined that the power transmission output changeinstruction is not an instruction instructing to increase the powertransmission output (NO in S602), the TX changes the power transmissionoutput based on the instructed change amount (S604), and advances theprocessing to S605.

In S605, the TX determines whether or not received power information hasbeen received from the RX (S605). If the received power information hasbeen received (YES in S605), the TX advances the processing to S606, andif the received power information has not been received (NO in S605),the TX advances the processing to S609. In S606, the TX determines,based on the received power information that has been received, whetheror not the received power has been reduced to a target value. Here, thetarget value may be set to received power that falls within the range ofthe GP before the re-execution of the negotiation, but is not limitedthereto. For example, the target value may be set to the received powerindicated by the last accepted calibration reference value information(to which an ACK has been transmitted), the maximum received power amongthe received powers indicated by pieces of calibration reference valueinformation that have been accepted in the past.

If it is determined that the received power has been reduced to thetarget value (YES in S606), the TX transmits an ACK (S607), and ends thepresent processing. On the other hand, if it is determined that thereceived power has not been reduced to the target value (NO in S606),the TX transmits a NAK (S608), and advances the processing to S609. InS609, the TX determines whether or not the enhanced calibrationreference value information has been received. If it is determined thatthe enhanced calibration reference value information has been received(YES in S609), the TX advances the processing to S610, and if it isdetermined that the enhanced calibration reference value information hasnot been received (NO in S609), the TX returns the processing to S601.As in the cases of the first calibration reference value information andthe second calibration reference value information, the TX determineswhether or not to accept the enhanced calibration reference valueinformation (S610). Then, if the TX accepts the enhanced calibrationreference value information (YES in S610), the TX transmits an ACK(S611), calculates an estimated value of power loss based on theenhanced calibration reference value information (S613), and ends thepresent processing. On the other hand, if the TX does not accept theenhanced calibration reference value information (NO in S610), the TXtransmits a NAK (S612), and returns the processing to S601. After thecompletion of the present processing, the TX advances the processing toS513, and thereafter repeatedly executes the processing shown in FIG. 5.

(Flow of Processing Executed by Power Reception Apparatus)

Next, an example of a flow of the processing executed by the RX will bedescribed. FIG. 7 shows an example of a flow of the processing executedby the RX. The present processing may be implemented, for example, bythe control unit 201 of the RX executing a program read from the memory209. At least part of the following processing may be implemented withhardware. The hardware in this case may be implemented, for example, byusing a predetermined compiler to automatically generate, from a programfor implementing processing steps, a dedicated circuit including a gatearray circuit such as an FPGA. The present processing may be executed inresponse to the RX being started as a result of the RX having beenturned on by the power supplied from the battery 202 or the TX, or inresponse to the user of the RX inputting an instruction to start awireless charging application. Alternatively, the present processing maybe started using another trigger.

After starting the processing, the RX executes processing defined as theSelection phase and the Ping phase in the WPC standard, and waits forself apparatus to be placed on the TX (S701). The RX detects that selfapparatus is placed on the TX, for example, by detecting the DigitalPing from the TX. If it is determined that self apparatus is placed onthe TX, the RX transmits, to the TX, identification information andcapability information, using communication in the Configuration phasedefined in the WPC standard (S702). After transmitting the RX transmitsthe identification information and the capability information, the RXdetermines a GP using communication in the Negotiation phase defined inthe WPC standard (S703). Here, because the communication for deviceauthentication has not been performed, the RX determines to perform anegotiation such that the GP is 5 W. Here, the RX performs, based on thedetermined GP, the communication in the Calibration phase of the WPCstandard described with reference to FIG. 9A. Upon completion of thecalibration, the RX start receiving power using the communication in thePower Transfer phase defined in the WPC standard (S705). After startingthe power reception, the RX performs the communication for deviceauthentication described with reference to FIG. 9B (S706). It is assumedthat this device authentication has succeeded. Thereafter, the RXperforms negotiation, and redetermines the value of the GP together withthe TX (S707). Since the device authentication has succeeded, in S707,the RX determines a value (e.g., 15 W) greater than 5 W as the GP. Afterredetermining the GP, the RX repeatedly executes the power receptioncontrol processing (S708). The RX transmits End Power Transfer of theWPC standard if an error has occurred, or if a fully charged state hasbeen reached. Accordingly, power transmission from the TX is stopped,and a series of processing for wireless charging ends.

Next, an example of a flow of the power reception control processingexecuted in S708 will be described with reference to FIG. 8. The presentprocessing may be implemented, for example, by the control unit 201 ofthe RX executing a program read from the memory 209. At least part ofthe following processing may be implemented with hardware. The hardwarein this case may be implemented, for example, by using a predeterminedcompiler to automatically generate, from a program for implementingprocessing steps, a dedicated circuit including a gate array circuitsuch as an FPGA.

After starting the processing, the RX determines whether or not thereceived power is smaller than the GP (S801). If it is determined thatthe received power is smaller than the GP (YES in S801), the RXincreases the power consumption (S802), transmits, to the TX, a powertransmission output change instruction instructing to increase the powertransmission output (S803), and advances the processing to S805. On theother hand, if it is determined that the received power is greater thanor equal to the GP (NO in S801), the RX does not change the powerconsumption, transmits, to the TX, a power transmission output changeinstruction instructing to maintain the power transmission output(S804), and advances the processing to S805.

In S805, the RX determines whether or not the transmission timing of theenhanced calibration reference value information has been reached. Here,the determination as to whether or not the transmission timing of theenhanced calibration reference value information has been reached may beperformed based on whether or not a predetermined time has elapsed aftercompletion of the negotiation. However, the present disclosure is notlimited thereto. For example, the RX may perform the determination inS805 based on whether or not the time elapsed after the TX completedcalculation of the estimated value of power loss and the RX received anACK to the calibration reference value information has reached apredetermined time. Alternatively, the RX may perform the determinationin S805 using an indicator other than an elapsed time. For example, theRX may determine whether or not the transmission timing of the enhancedcalibration reference value information has been reached based onwhether or not the difference between the received power upon completionof the negotiation and the present received power is greater than orequal to a threshold. The RX may determine whether or not thetransmission timing of the enhanced calibration reference valueinformation has been reached, using the difference between the receivedpower indicated by the calibration reference value information to whichan ACK has been most recently received, and the present received power.This allows the RX to reliably transmit the enhanced calibrationreference value information to the TX, if there is a certain amount ofchange in the received power, or in other words, if it is envisaged thatthe estimated value of power loss in the TX has a large error.

If it is determined that the transmission timing of the enhancedcalibration reference value information has been reached (YES in S805),the RX transmits enhanced calibration reference value informationincluding the present received power (S806), and determines whether ornot a NAK has been received from the TX (S807). If it is determined thata NAK to the transmitted enhanced calibration reference valueinformation has been received from the TX (YES in S807), the RXretransmits the enhanced calibration reference value information (S806).If the NAK has been received, the RX may perform, using the display unit207, performs display to prompt the user to, for example, re-place theRX. Accordingly, in the case where the power transmission in the TX isunstable, for example, due to the positional displacement of the RX, itis possible to re-execute predetermined processing for startingcharging, thus restarting stable charging. On the other hand, if an ACKhas been received to the enhanced calibration reference valueinformation (NO in S807), the RX ends the present processing, withoutdoing anything.

On the other hand, if it is determined that the transmission timing ofthe enhanced calibration reference value information has not beenreached (NO in S805), the RX transmits the received power information tothe TX, for example, at a predetermined time interval (S808), anddetermines whether or not a NAK has been received from the TX (S809). Ifa NAK to the transmitted received power information has been receivedfrom the TX (YES in S809), the RX reduces the power consumption (S810),transmits, to the TX, a power transmission output change instructioninstructing to reduce the power transmission output of the TX (S811),and ends the present processing. On the other hand, if an ACK to thereceived power information has been received from the TX (NO in S809),the RX ends the present processing, without doing anything.

As a result of the RX periodically transmitting the enhanced calibrationreference value information in an increasing phase or a decreasing phaseof the power transmission output, it is possible to prevent asignificant deviation between the received power of the calibrationreference value and the actual received power. For example, when thepower transmission output is increasing, if the calibration referencevalue information is notified to the TX from the RX within a certainperiod, the TX can obtain a new calibration reference value that ishigher than the received powers of the previously obtained calibrationreference values, and that does not significantly deviate from thereceived powers of these calibration reference values. Similarly, whenthe power transmission output is decreasing, if calibration referencevalue information is notified to the TX from the RX within a certainperiod, the TX can obtain a new calibration reference value that islower than the received powers of the previously obtained calibrationreference values, and that does not significantly deviate from thereceived powers of these calibration reference values. Also, by usingsuch a new calibration reference value, the TX can accurately estimatethe power loss as compared with when no such calibration reference valueis available. In general, when the difference between the received powerof the calibration reference value and the actual received powerincreases, it is anticipated that the error in estimation of the powerloss also increases. In this respect, by notifying the calibrationreference value information corresponding to the present received powerto the TX from the RX within a certain period, the TX can obtainreceived power of a calibration reference value in a range that does notdeviate from the received power of the existing calibration referencevalue above a certain level. As a result, for example, the TX canthoroughly obtain a wide range of calibration reference values forreceived power, so that the RX will not receive power that significantlydeviates from the received power corresponding to the calibrationreference value. This makes it possible to accurately estimate the powerloss for any received power, thus preventing erroneous detection of aforeign object, and failure in detecting a foreign object that ispresent. If the TX is unable to obtain the enhanced calibrationreference value information within a certain period in an increasingphase or a decreasing phase of the power transmission output, there is apossibility that the present received power significantly deviates fromthe received power of the calibration reference value. For this reason,timeout determination can be used, and the TX may be configured to notto increase (or reduce) the power transmission output if a timeout hasoccurred, and it is thus possible to prevent powertransmission/reception with power that may reduce the accuracy offoreign object detection.

The processing operations associated with the timeout described abovemay be executed only in a situation where the power transmission outputincreases (or decreases) to such a degree that the received power in theRX exceeds the received power of the existing calibration referencevalue. The reason being that if the received power is within the rangeof the received power of the existing calibration reference value,accurate estimation of power loss can be performed without having toobtain an additional calibration reference value. The TX may set anexpiration period for each of the calibration reference values, forexample. Also, the TX may discard a reference value that has passed theset expiration period, and execute the above-described processing. Forexample, if the power transmission output is to be increased/decreasedsuch that the received power changes beyond the range of the receivedpower specified by the reference value that is held in the TX, the TXmay execute the processing operations associated with the timeoutdescribed above.

(Flow of Processing Executed in System)

An operating sequence for a case where the TX and the RX execute theabove-described processing will be described, assuming severalsituations. It is assumed that, in the initial state, the RX is notplaced on the TX, and the TX has power transmission capabilitysufficient to execute power transmission with the GP requested from theRX.

Processing Example 1

First, a first processing example will be described with reference toFIGS. 10A and 10B. In the present processing example, the GP isdetermined as 5 W in the initial negotiation, and power transmission isstarted. Then, after the power transmission has been started, deviceauthentication succeeds, and the GP is redetermined as 15 W byre-executing the negotiation. Using the completion of the negotiation asa trigger, or in other words, using, as a trigger, the transmission ofan ACK to SRQ/en, the TX starts the timer. Also, it is assumed that,while the received power in the RX changes from 5 W to 15 W, the TX canneither receive the enhanced calibration reference value information andnor transmit an ACK within a predetermined time. At this time, the TX ofthe present processing example reduces the power transmission output,with the GP range before device authentication, which is 5 W, as atarget value.

The TX waits for an object to be placed, using an Analog Ping (S401,F1001). As a result of the RX being placed (F1002), a change occurs inthe Analog Ping (F1003), whereby the TX detects that an object is placed(F1004). From the subsequent Digital Ping, the RX detects that selfapparatus is placed on the TX (S701, F1005, F1006). From a response tothe Digital Ping, the TX detects that the object placed thereon is theRX. Subsequently, using communication in the Configuration phase, the TXobtains the identification information and the capability informationfrom the RX (S402, S702, F1007). Next, the TX and the RX performcommunication in the Negotiation phase (S403, S703, F1008). At thispoint, device authentication has not succeeded, and therefore the GP isdetermined as 5 W in this negotiation.

Subsequently, the TX and the RX start communication in the Calibrationphase (S404, S704). In the communication in the Calibration phase, theTX receives, from the RX, first calibration reference value informationindicating that the received power is 500 mW (F1009). Then, for example,as a result of determining that its own power transmission state isstable, the TX determines to accept the first calibration referencevalue information, and transmits an ACK (F1010). Next, the TX receives,from the RX, a power transmission output change instruction instructingto increase the power transmission output (F1011), and increases thepower transmission output in accordance with the instruction (F1012).Thereafter, the TX receives, from the RX, second calibration referencevalue information indicating that the received power is 5 W (F1013). Forexample, as a result of determining that its own power transmissionstate is stable, the TX determines to accept the second calibrationreference value information, and transmits an ACK (F1015). In addition,the TX calculates an estimated value of power loss, based on the firstcalibration reference value information and the second calibrationreference value information (F1014). By the transmission of an ACK inF1015, the Power Transfer phase is started (S405, S705). Subsequently,communication for device authentication is performed (S406, S706,F1016). It is assumed that this device authentication has succeeded. Ifthe device authentication has succeeded, the TX and the RX re-executethe communication in the Negotiation phase, and the GP is redetermined(S407, S707, F1017). Here, it is assumed that the GP is redetermined as15 W. After the GP had been redetermined, the TX and the RX start thepower transmission control processing and the power reception controlprocessing, respectively (S408, S708).

After starting the power transmission control processing, the TX startsa timer set to the completion of calculation of an estimated value ofpower loss (S501, F1018). If a power transmission output changeinstruction instructing to increase the power transmission output isreceived from the RX, the TX increases the power transmission output inaccordance with the instruction (S503, S802, S803, F1019, F1020).Subsequently, the TX receives, from the RX, received power informationindicating that the received power is 15 W (S808, F1021), and transmitsan ACK to the received power information (S505, F1022). If a powertransmission output change instruction instructing not to change thepower transmission output is received from the RX (S804, F1023), the TXfollows the instruction, and does not change the power transmissionoutput. Thereafter, the TX determines that a timeout has occurred, forexample, using, as a trigger, the passage of a predetermined time sincethe start of the timer without the enhanced calibration reference valueinformation being received, and starts the timeout processing (S512,F1024). After starting the timeout processing, if received powerinformation indicating that the received power is 15 W is received fromthe RX (S808, F1025), the TX transmits a NAK in order to reduce thereceived power in the RX to 5 W, which is the target value (S608,F1026). The RX reduces the power consumption (S810, F1027), andtransmits, to the TX, a power transmission output change instructioninstructing to reduce the power transmission output (S811, F1028). Ifthe power transmission output change instruction is received, the TXreduces the power transmission output in accordance with the instruction(S604, F1029). Subsequently, if received power information indicatingthat the received power is 10 W is received from the RX (S808, F1030),the TX transmits a NAK in order to cause the RX to continue reducing thereceived power because the received power is higher than 5 W, which isthe target value (S608, F1031). The RX reduces the power consumption(S810, F1032), and transmits, to the TX, a power transmission outputchange instruction instructing to reduce the power transmission output(S811, F1033). If this power transmission output change instruction isreceived, the TX reduces the power transmission output in accordancewith the instruction (S604, F1034). Thereafter, if received powerinformation indicating that the received power is 5 W is received (S808,F1035), the TX transmits an ACK to the RX because the received power isgreater than or equal to 5 W, which is the target value, and continuesthe power transmission with that output (S607, F1036).

According to the above-described operation, if an estimated value ofpower loss cannot be calculated after fast charging with a relativelyhigh power transmission output has been started, the TX reduces thepower transmission output to the output range before the start of fastcharging. This makes it possible to continue power transmission andreception with an appropriate power transmission output, while assumingthe possibility of occurrence of erroneous detection or detectionfailure of a foreign object. As a result of the RX periodicallytransmitting the enhanced calibration reference value information in anincreasing phase or a decreasing phase of the power transmission output,it is possible to prevent a significant deviation between the receivedpower of the calibration reference value and the actual received power.Accordingly, it is possible to accurately estimate power loss forreceived power that has been increased or reduced, thus preventingerroneous detection of a foreign object and failure in detecting aforeign object that is present. It is determined that a timeout hasoccurred if the TX is not able to obtain enhanced calibration referencevalue information within a certain period in an increasing phase or adecreasing phase of the power transmission output, and TX does notincrease (or reduces) the power transmission output. This makes itpossible to prevent power transmission and reception with power that mayreduce the accuracy of foreign object detection.

Processing Example 2

Next, a second processing example will be described with reference toFIGS. 11A and 11B. In the present processing example, when a timeout hasoccurred, the TX reduces the power transmission output, using, as atarget value, received power indicated by the immediately previouslyobtained valid enhanced calibration reference value information, unlikein Processing Example 1. Here, it is assumed that, when the receivedpower in the RX changed from 5 W to 10 W after the GP has beendetermined, the TX receives enhanced calibration reference valueinformation indicating that the received power of the RX is 10 W,calculates an estimated value of power loss, and transmits an ACK. Inthis case, the TX resets the timer, using as, a trigger, thetransmission of the ACK, and starts the timer again. It is assumed that,thereafter, the received power in the RX changed from 10 W to 15 W, butthe TX was not able to receive the enhanced calibration reference valueinformation within a predetermined time. In this case, the TX reducesthe power transmission output, using, as a target value, 10 W, which isthe received power indicated by the last obtained valid enhancedcalibration reference value information.

The processing operations in F1101 to F1120 are the same as those inF1001 to F1020 in FIGS. 10A and 10B. Therefore, descriptions of theseprocessing operations have been omitted.

In F1121, the RX transmits, to the TX, received power informationindicating that the received power is 7 W (S808). If the received powerinformation is received, the TX transmits an ACK because a timeout hasnot occurred at this point (S505, F1122). Since the received power hasnot reached the GP, the RX thereafter transmits, to the TX, a powertransmission output change instruction instructing to increase the powertransmission output (S802, S803, F1123). If the power transmissionoutput change instruction is received, the TX increases the powertransmission output in accordance with the instruction (S503, F1124).

Thereafter, the RX transmits, to the TX, enhanced calibration referencevalue information in response to the occurrence of a transmission timingof the enhanced calibration reference value information (S806, F1125).Here, the enhanced calibration reference value information indicatesthat the received power in the RX is 10 W. IF the enhanced calibrationreference value information is received, the TX determines to accept thecalibration reference value information, for example, as a result ofdetermining that its own power transmission state is stable, calculatesan estimated value of power loss (S508, F1126), and transmits an ACK(S509, F1127).

After transmitting the ACK, the TX resets the timer, and starts thetimer again (S513, S501, F1128, F1129). Thereafter, the RX transmits, tothe TX, received power information indicating that the received power is13 W (S808, F1130). If the received power information has been receivedbefore the timer expires, the TX transmits an ACK (S505, F1131).Thereafter, the TX determines that a timeout has occurred, using, as atrigger, the passage of a predetermined time since the start of thetimer in F1129 without the enhanced calibration reference valueinformation being received, and starts the timeout processing (S512,F1132).

Since the received power has not reached the GP, the RX thereaftertransmits, to the TX, a power transmission output change instructioninstructing to increase the power transmission output (S802, S803,F1133). The TX receives the power transmission output changeinstruction, but does not follow the instruction because a timeout hasalready occurred, and does not change the power transmission output(S603, F1134). After this, the RX transmits, to the TX, received powerinformation indicating that the received power is 13 W (S808, F1135). Ifthe received power information is received, the TX transmits a NAK tothe RX to cause the RX to reduce the received power to 10 W, which isthe target value, because the timeout processing has already beenstarted (S608, F1136). If the NAK is received, the RX reduces the powerconsumption (S810, F1137), and transmits, to the TX, a powertransmission output change instruction instructing to reduce the powertransmission output (S811, F1138). If the power transmission outputchange instruction is received, the TX reduces the power transmissionoutput in accordance with the instruction (S604, F1139). Thereafter, theRX transmits, to the TX, received power information indicating that thereceived power has been reduced to 10 W as a result of the reduction inthe power transmission output (S808, F1140). If the received powerinformation indicating that the received power is 10 W is received, theTX transmits an ACK because the received power has been reduced to 10 W,which is the target value, or less (S607, F1041). Then, the TX continuesthe power transmission, while maintaining the power transmission output.

According to the above-described operation, if an estimated value ofpower loss cannot be calculated after fast charging with a relativelyhigh power transmission output has been started, the TX reduces thepower transmission output such that received power for which anestimated value of power loss has been calculated can be obtained. Thismakes it possible to continue power transmission and reception with anappropriate power transmission output, while assuming the possibility ofoccurrence of erroneous detection or detection failure of a foreignobject. As a result of the RX periodically transmitting the enhancedcalibration reference value information in an increasing phase or adecreasing phase of the power transmission output, it is possible toprevent a significant deviation between the received power of thecalibration reference value and the actual received power. Accordingly,it is possible to accurately estimate power loss for received power thathas been increased or reduced, thus preventing erroneous detection of aforeign object and failure in detecting a foreign object that ispresent. It is determined that a timeout has occurred if the TX is notable to obtain enhanced calibration reference value information within acertain period in an increasing phase or a decreasing phase of the powertransmission output, and TX does not increase (or reduces) the powertransmission output. This makes it possible to prevent powertransmission and reception with power that may reduce the accuracy offoreign object detection.

The TX may start the above-described timer at a timing before there-execution of the device authentication and the negotiation. Forexample, the TX may start the timer, using, as a trigger, the completionof calibration as a result of receiving the second calibration referencevalue information, or in other words, using, as a trigger, thetransmission of an ACK to the second calibration reference valueinformation. At this time, the TX may start the timer if the calibrationhas been completed with received power (e.g., 3 W) that is smaller than5 W, which is the GP determined with a power reception apparatus thathas not succeeded in device authentication. Then, if the TX is not ableto receive enhanced calibration reference value information (e.g.,indicating that the received power is 5 W, or the like) within apredetermined time, the TX reduces the power transmission output, using,as a target value, received power of 3 W indicated by the secondcalibration reference value information. By reducing the powertransmission output to the output used at the time of completion of thecalibration, which is before the start of fast charging, in this manner,it is possible to continue power transmission and reception with anappropriate output in a state in which the power transmission output issmall, and thus error variation in general tends to be large.

The TX may start the above-described timer, using, as a trigger, theamount of change in received power becoming greater than or equal to athreshold. That is, the TX may be configured to not to execute theprocessing operations associated with the timeout shown in FIG. 5, orFIGS. 6A and 6B, before the amount of change in received power becomesgreater than or equal to a threshold. For example, the TX may start thetimer, using, as a trigger, the reception of received power informationor calibration reference value information indicating that the amount ofchange in received power from the received power immediately after thecompletion of the calibration is greater than or equal to a threshold,or using, as a trigger, the transmission of a response to the receivedpower information or calibration reference value information. The TX maystart the timer, using, as a trigger, the reception of received powerinformation or calibration reference value information indicating thatthe amount of change in received power from the received power when thevalid enhanced calibration reference value information is obtained isgreater than or equal to a threshold, or using, as a trigger, thetransmission of a response to the received power information orcalibration reference value information. The TX may start the timer,using, as a trigger, the reception of received power information orcalibration reference value information indicating that the amount ofchange in received power from any of the received powers indicated bythe valid calibration reference value information is greater than orequal to a threshold, or using, as a trigger, the transmission of aresponse to the received power information or calibration referencevalue information. Accordingly, in the case where the change from thereceived power for which an estimated value of power loss has beencalculated is insignificant, and thus the accuracy of foreign objectdetection is considered to be sufficiently ensured, it is possible tosuppress the occurrence of unnecessary timeout and unnecessary changingof the power transmission output. As the threshold for the amount ofchange in received power, a predetermined fixed value may be used, or avalue determined between the TX and the RX using any communicationperformed before starting the Power Transfer phase may be used. The TXmay be configured to not to execute the processing operations associatedwith the timeout shown in FIG. 5, or FIGS. 6A and 6B, before the amountof change in received power after the valid enhanced calibrationreference value information has been obtained becomes greater than orequal to a threshold.

The TX may start the above-described timer, using, as a trigger, theamount of change in power transmission output becoming greater than orequal to a threshold. That is, the TX may be configured to not toexecute the processing operations associated with the timeout shown inFIG. 5, or FIGS. 6A and 6B, before the amount of change in powertransmission output becomes greater than or equal to a threshold. Forexample, the TX may start the timer, using, as a trigger, the amount ofchange from the power transmission output immediately after thecompletion of the calibration becoming greater than or equal to athreshold, or using, as a trigger, the amount of change in powertransmission output from the power transmission output when the validcalibration reference value information is obtained becoming greaterthan or equal to a threshold. In an example, the TX may start the timerif a value that is increased by 1 when the power transmission output isincreased by the above-described power transmission output changeinstruction, and that is reduced by 1 when the power transmission outputis reduced by the power transmission output change instruction, hasreached a predetermined positive value or a predetermined negativevalue. In the case where a value indicating the amount by which thepower transmission output is to be changed by the power transmissionoutput change instruction is designated, the TX may cumulatively add thedesignated value, and may start the timer when the value has reached apredetermined positive value or a predetermined negative value. The TXmay monitor its own power transmission output, and may start the timer,using, as a trigger, the amount of change reaching a predeterminedvalue. Accordingly, in the case where the change in power transmissionoutput and also the change in received power after an estimated value ofpower loss has been calculated are assumed to be insignificant, it ispossible to suppress the occurrence of unnecessary timeout andunnecessary changing of the power transmission output. The TX may beconfigured to not to execute the processing operations associated withthe timeout shown in FIG. 5, or FIGS. 6A and 6B, before the amount ofchange in power transmission output after the valid enhanced calibrationreference value information has been obtained becomes greater than orequal to a threshold.

The TX may start the above-described timer, using, as a trigger, thereception of the enhanced calibration reference value information afteran estimated value of power loss has been calculated. That is, the TXmay be configured to not to execute the processing operations associatedwith the timeout shown in FIG. 5, or FIGS. 6A and 6B, before enhancedcalibration reference value information is received. Accordingly, atimeout can be provided only when the RX intends to calculate anestimated value in the case where foreign object detection can beperformed using a calculated estimated value of power loss. This makesit possible to suppress the occurrence of unnecessary timeout, andunnecessary changing of the power transmission output.

The enhanced calibration reference value information may be transmittedwhen performing power transmission and reception that falls outside therange of the received reference value of received power. In this case,the expression “falls outside the range of . . . reference value”includes both falling below a lower limit that defines the range, andexceeding an upper limit that defines the range of the reference value.

The enhanced calibration reference value information may be transmittedif the GP is increased as a result of device authentication(Authentication) using an electronic certificate on the powertransmission apparatus, or device authentication (Authentication) usingan electronic certificate on the power reception apparatus havingsucceeded.

For example, in the case where power transmission and reception isperformed for an extended period of time, the accuracy of the foreignobject detection processing using a calibration reference value obtainedin the calibration phase may be reduced due to an influence of heatgeneration or the like. For this reason, if a certain amount of time haselapsed after the calibration reference value has been obtained, acalibration reference value may be obtained as the enhanced calibrationreference value information. For example, the TX may request theenhanced calibration reference value information from the RX.

The enhanced calibration reference value information may be transmittedif the received power in the power reception apparatus changes to avalue exceeding a predetermined value.

The TX need not start the above-described timer if a predeterminedcondition is satisfied. That is, the TX may be configured to not toexecute the processing operations associated with the timeout shown inFIG. 5, or FIGS. 6A and 6B, while a predetermined is not satisfied. TheTX may be configured to not to start the timer, for example, if powertransmission and reception is performed with received power closer tothe received power indicated by the valid calibration reference valueinformation obtained in the past, or if power transmission and receptionis performed with received power within a range in which an estimatedvalue is calculated using a plurality of pieces of calibration referencevalue information. The TX may be configured to not to start the timer ifthe number of times that an estimated value has been calculated usingthe valid calibration reference value information obtained in the pastbecomes greater than or equal to a predetermined number of times.Accordingly, in the case where the accuracy of foreign object detectionis sufficiently ensured, it is possible to suppress the occurrence ofunnecessary timeout and unnecessary changing of the power transmissionoutput.

In the above-described example, after a timeout has occurred, the targetvalue is set within the range of the received power for which anestimated value of power loss has been calculated. However, receivedpower that is outside the aforementioned range and whose difference fromthe received power for which an estimated value of power loss has beencalculated is less than a threshold may be used as the target value.This makes it possible to continue charging that is as fast as possiblewithout significantly affecting the accuracy of foreign object detectionusing a calculated estimated value.

In the above-described example, after a timeout has occurred, the TXchanges the power transmission output such that the received power hasthe target value. However, a negotiation may be performed again betweenthe TX and the RX, and the GP may be changed to the target value. Atthis time, the negotiation is performed such that the target value is avalue within the range from a minimum value to a maximum value of thereceived power indicated by the valid calibration reference valueinformation. Accordingly, a maximum value of the received power that canbe received by the RX can be kept at a target value or less, thus makingit possible to continue charging while suppressing a reduction in theaccuracy of foreign object detection.

After a timeout has occurred, the TX may determine that some problemoccurs in the charging processing, and stop the power transmission. Thismakes it possible to suppress the occurrence of a problem caused by anundetected foreign object, erroneous operation, or the like. Afterstopping the power transmission, the TX may return the processing to theSelection phase in S401. Accordingly, if it is difficult to continuepower transmission, for example, due to the positional displacement ofthe RX, it is possible to re-execute predetermined processing forstating charging, thus resuming charging appropriately. If anabnormality is detected, the TX may limit power transmission so as toreduce the power to be transmitted.

In the above-described example, after a timeout has occurred, the TXtransmits a NAK to the RX to the received power information in order tochange the power transmission output such that the received power hasthe target value. At this time, the TX may transmit a response includingadditional information. For example, the TX may include, in the NAK tobe transmitted, a notification to change the power transmission output,a reason for changing the power transmission output, the target value ofreceived power, a criterion for determining a timeout, a request fortransmission of additional calibration reference value information, andso forth. These pieces of information may be transmitted using aseparate response signal/message that is different from the NAK. Allpieces of the additional information may be transmitted using oneresponse signal or message, or the additional information may betransmitted using a plurality of response signals or messages in adistributed manner. Such additional information allows the RX to use,for example, the display unit 207 to notify, via a display or the like,the user that fast charging is limited, and it is thus possible toimprove the user convenience. Furthermore, the RX can transmitadditional calibration reference value information, using the receptionof the additional information as a trigger, and it is thus possible toavoid changing of the power transmission output in the TX, and continuefast charging.

After a timeout has occurred, the TX may use the display unit 307 tomake an inquiry to the use as to whether or not to continue fastcharging, and may determine whether or not to change the powertransmission output in accordance with an instruction received via theoperation unit 308. For example, the TX may be configured to transmit anACK to the received power information without changing the powertransmission output, if an instruction to continue fast charging isgiven within a predetermined time since the inquiry has been started.This processing may be performed using the display unit 207 and theoperation unit 208 of the RX. For example, the RX may be configured tostart the inquiry to the user, using, as a trigger, the reception of theabove-described additional information, and may be configured to not totransmit a power transmission output change instruction instructing toreduce the power transmission output, if an instruction to continue fastcharging is given within a predetermined time. Accordingly, in the casewhere the user can determine that incorporation of a foreign object orthe like has not occurred, it is possible to suppress unnecessarychanging of power transmission output, thus continuing fast charging.

In the above-described example, when increasing the received power inthe RX, the power transmission output is reduced (or not increased) ifthe calibration reference value information has not been accepted for apredetermined time or longer. The same processing may also be executedwhen reducing the received power in the RX. That is, the target valuefor changing the power transmission output may be received power that islarger than the received power at that time, and the TX may increase thepower transmission output such that the received power in the RX isincreased. For example, the TX may use, as the target value, the largestreceived power of all the received powers indicated by the validcalibration reference value information obtained in the past. In thiscase, the RX transmits, to the TX, a power transmission output changeinstruction instructing to increase the power transmission output. Thismakes it possible to continue charging that is as fast as possible, withreceived power that enables accurate detection of a foreign object.

In the above-described example, the TX calculates an estimated value ofpower loss. However, the present disclosure is not limited thereto. Thatis, the TX need only obtain information for associating a powertransmission output and received power in the RX that can be obtained atthe power transmission output. For example, the TX need only obtain acombination of received power Pr1 of a first calibration reference valueand a power transmission output Pt1 at that time, and a combination ofreceived power Pr2 of a second calibration reference value and a powertransmission output Pt2 at that time. In this case as well, for example,for received power Pr3 between Pr1 and Pr2, a value obtained by(Pt2−Pt1)/(Pr2−Pr1)×(Pr3−Pr1)+Pt1, and the actual transmission power maybe compared, and it can be detected that a foreign object is present, ifthe absolute value of the difference exceeds a predetermined value.

According to the present disclosure, it is possible to improveconvenience of wireless power transfer.

Other Embodiments

Embodiment(s) of the present disclosure can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present disclosure has been described with reference toexemplary embodiments, it is to be understood that the presentdisclosure is not limited to the disclosed exemplary embodiments. Thescope of the following claims is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures and functions.

1. A power transmission apparatus comprising: a power transmission unitconfigured to wirelessly transmit power to a power reception apparatus;a communication unit configured to communicate with the power receptionapparatus; a processing unit configured to execute, when wirelesslytransmitting power using the power transmission unit, detectionprocessing for detecting an object different from the power receptionapparatus, using a power loss; an obtaining unit configured to obtain,using the communication unit, from the power reception apparatus,reference value information regarding a reference value of receivedpower that is used to obtain the power loss; and a control unitconfigured to perform a specific control after the power loss has beenobtained and in a case where a predetermined time has elapsed since apredetermined timing associated with a timing at which information isobtained from the power reception apparatus, without obtaining thereference value information that is valid, the specific control being acontrol to prevent an output power using the power transmission unitfrom being increased, regardless of received power of the powerreception apparatus.
 2. The power transmission apparatus according toclaim 1, wherein the predetermined timing is determined based on atiming at which the valid reference value information is obtained fromthe power reception apparatus, or a timing at which the communicationunit transmits a positive acknowledgement to the power receptionapparatus, the positive acknowledgement representing that the referencevalue information has been accepted in response to obtaining thereference value information from the power reception apparatus.
 3. Thepower transmission apparatus according to claim 1, wherein thepredetermined timing is determined based on a timing at which it isdetermined that a difference between the received power represented bythe reference value information obtained using the communication unit,and received power represented by the valid reference value informationobtained in the past is greater than or equal to a threshold, or atiming at which a positive acknowledgement representing that thereference value information has been accepted is transmitted to thepower reception apparatus.
 4. The power transmission apparatus accordingto claim 1, wherein the communication unit receives received powerinformation that is different from the reference value information andrepresents the received power of the power reception apparatus, and thepredetermined timing is determined based on a timing at which it isdetermined that a difference between the received power represented bythe received power information and received power represented by thevalid reference value information obtained in the past is greater thanor equal to a threshold, or a timing at which a response to the receivedpower information is transmitted to the power reception apparatus. 5.The power transmission apparatus according to claim 1, wherein thecontrol unit controls an output power in response to the communicationunit receiving a change instruction instructing to change the outputpower from the power reception apparatus, and the predetermined timingis determined based on a timing at which an amount of change in theoutput power caused by the change instruction, from the output powerwhen the valid reference value information is obtained, is greater thanor equal to a threshold, or a timing at which a response to the changeinstruction is transmitted to the power reception apparatus.
 6. Thepower transmission apparatus according to claim 1, wherein thepredetermined timing is determined based on a timing at whichinformation is received from the power reception apparatus via thecommunication unit, or a timing at which a response to the informationfor ending the negotiation is transmitted via the communication unit,the information being information for ending a negotiation for receivedpower that the power reception apparatus is to obtain through powertransmission.
 7. The power transmission apparatus according to claim 1,wherein the control unit does not perform the specific control while thepredetermined timing is not determined.
 8. The power transmissionapparatus according to claim 1, wherein the control unit counts thenumber of times that a response has been transmitted while the validreference value information is not obtained after the predeterminedtiming, the response representing that the communication unit does notaccept the reference value information despite receiving the referencevalue information, and performs the specific control if the number oftimes has reached a predetermined number of times.
 9. The powertransmission apparatus according to claim 1, wherein the control unitcounts the number of times that information different from the referencevalue information is received from the power reception apparatus whilethe valid reference value information is not obtained after thepredetermined timing, and performs the specific control if the number oftimes has reached a predetermined number of times.
 10. The powertransmission apparatus according to claim 9, wherein the informationdifferent from the reference value information is received powerinformation representing the received power of the power receptionapparatus, or a change instruction instructing to change an output powerfrom the power reception apparatus.
 11. The power transmission apparatusaccording to claim 1, wherein, in the specific control, the control unitreduces the output power until the received power of the power receptionapparatus is reduced to received power represented by the validreference value information.
 12. The power transmission apparatusaccording to claim 1, further comprising an execution unit configured toexecute authentication with the power reception apparatus, wherein, inthe specific control, the control unit reduces the output power untilthe received power of the power reception apparatus is reduced toreceived power that is to be obtained in an apparatus that has notsucceeded in authentication.
 13. The power transmission apparatusaccording to claim 11, wherein, in a case where the received powerinformation representing the received power of the power receptionapparatus has been received from the power reception apparatus, thecontrol unit reduces the output power by causing the communication unitto transmit a negative acknowledgement, thereby controlling the powerreception apparatus to transmit a change instruction instructing toreduce the output power.
 14. The power transmission apparatus accordingto claim 1, wherein, while the specific control is performed, thecontrol unit prevents the output power using the power transmission unitfrom being increased even if a change instruction instructing toincrease the output power has been received from the power receptionapparatus using the communication unit.
 15. The power transmissionapparatus according to claim 1, wherein, in the specific control, thecontrol unit performs, via the communication unit, a negotiation forreceived power that the power reception apparatus is to obtain throughpower transmission.
 16. The power transmission apparatus according toclaim 15, wherein the negotiation for the received power in the specificcontrol is performed based on the received power represented by thevalid reference value information.
 17. The power transmission apparatusaccording to claim 1, wherein, in the specific control, the control unitstops power transfer performed by the power transmission unit.
 18. Thepower transmission apparatus according to claim 1, wherein the obtainingunit further obtains predetermined information for associating, based onthe valid reference value information, an output power using the powertransmission unit with received power corresponding to the output power.19. A power transmission method performed using a power transmissionapparatus including a power transmission unit configured to wirelesslytransmit power to a power reception apparatus; and a communication unitconfigured to communicate with the power reception apparatus, the methodcomprising: when wirelessly transmitting power using the powertransmission unit, executing detection processing for detecting anobject different from the power reception apparatus, using a power loss;obtaining, using the communication unit, from the power receptionapparatus, reference value information regarding a reference value ofreceived power that is used to obtain the power loss; and performing aspecific control after the power loss has been obtained and in a casewhere a predetermined time has elapsed since a predetermined timingassociated with a timing at which information is obtained from the powerreception apparatus, without obtaining the reference value informationthat is valid, the specific control being a control to prevent an outputpower using the power transmission unit from being increased, regardlessof received power in the power reception apparatus.
 20. A non-transitorycomputer-readable storage medium that stores a program for causing acomputer included in a power transmission apparatus, which includes apower transmission unit configured to wirelessly transmit power to apower reception apparatus; and a communication unit configured tocommunicate with the power reception apparatus, to: when wirelesslytransmitting power using the power transmission unit, execute detectionprocessing for detecting an object different from the power receptionapparatus, using a power loss; obtain, using the communication unit,from the power reception apparatus, reference value informationregarding a reference value of received power that is used to obtain thepower loss; and perform a specific control after the power loss has beenobtained and in a case where a predetermined time has elapsed since apredetermined timing associated with a timing at which information isobtained from the power reception apparatus, without obtaining thereference value information that is valid, the specific control being acontrol to prevent an output power using the power transmission unitfrom being increased, regardless of received power in the powerreception apparatus.